1. The Field of the Invention
The present invention relates generally to electronic circuitry and, more particularly, to closed loop Direct Current (DC) to DC current converters.
2. Background and Relevant Art
Many typical integrated semiconductor devices operate using standard supply voltages that are set to promote reliability and performance for a given technology. For example, semiconductor circuits typically have access to a relatively low supply voltage (often referred to as VSS) and to a relatively high supply voltage (often referred to as VDD). However, it is often advantageous to provide even higher supply voltages for high voltage devices. For example, a high voltage transistor may be added to the standard Complementary Metal-Oxide-Semiconductor (CMOS) process to allow for switching of higher voltages than the standard technology is designed to handle. As an additional example, embedded Electronically Erasable and Programmable Read-Only-Memory (EEPROM) may be added to the standard CMOS technology. EEPROMs typically use higher voltages to program and erase than provided by the standard technology.
Direct Current (DC) to Direct Current (DC) converters (also referred to herein as “DC-to-DC converters”) up-convert the supply voltages when higher voltages are needed. There are several conventional DC-to-DC converter types, most of which have high output impedances. Therefore, DC-to-DC converters are typically designed to generate a higher voltage than needed. The output DC voltage of the DC-to-DC converter is thus regulated to a desired voltage by a feedback system. An example of such a DC-to-DC converter is illustrated in FIG. 2 as closed loop DC-to-DC converter 200.
The closed loop DC-to-DC converter 200 includes an open loop DC-to-DC converter 210, an output capacitor 220, and a feedback system 230. The open loop DC-to-DC converter 210 is capable of using the standard high voltage reference VDD to generate an even higher output voltage Vout on its output terminal OUT. If the open loop DC-to-DC converter 210 is operating at maximum power continuously, then its output voltage Vout will be higher than needed. The feedback system 230 enables and disables the open loop DC-to-DC converter 210 as appropriate so that the output voltage Vout is regulated about its desired value.
The feedback system 230 includes a series of two resistors 231 and 232 and a comparator 233. The two resistors 231 and 232 are configured in series between the output terminal OUT and ground so as to voltage divide the output voltage Vout. The negative input terminal of the comparator 233 receives the voltage divided voltage from between the resistors 231 and 232. The positive input terminal of the comparator 233 receives a reference voltage Vref. If the output voltage Vout, is below its desired value, then the reference voltage Vref is greater than the voltage divided voltage. In that case, the comparator 233 enables (or causes to remain enabled) the open loop DC-to-DC converter 210 thereby increasing the output voltage Vout. If the output voltage Vout is above its desired value, then the voltage divided voltage is greater than the reference voltage Vref. In that case, the comparator 233 disables (or causes to remain disabled) the open loop DC-to-DC converter 210 thereby decreasing the output voltage Vout as charge drains through the resistors 231 and 232.
The closed loop DC-to-DC converter 200 requires a reference voltage Vref, which requires additional power and additional layout area on the integrated chips. Furthermore, the resistors 231 and 232 places a load on the DC-to-DC converter 200 since, as previously mentioned, current drains through the resistors 231 and 232 regardless of the output voltage Vout level. DC-to-DC converters typically have low power efficiencies so the current drain on the high supply voltage Vout will be several times greater than the current drain through the resistors 231 and 232.
Accordingly, what would be advantageous would be a DC-to-DC converter that has a regulated closed loop feedback system that does not require a reference voltage and that reduced the load on the output of the DC-to-DC converter.